7. A particle is travelling along the \(x\)-axis. At time \(t = 0\), the particle is at \(O\) and it travels such that its velocity, \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\), at a distance \(x\) metres from \(O\) is given by $$v = \frac { 2 } { x + 1 }$$ The acceleration of the particle is \(a \mathrm {~ms} ^ { - 2 }\).

1. Show that \(a = \frac { - 4 } { ( x + 1 ) ^ { 3 } }\).
   (4 marks) The points \(A\) and \(B\) lie on the \(x\)-axis. Given that the particle travels \(d\) metres from \(O\) to \(A\) in \(T\) seconds and 4 metres from \(A\) to \(B\) in 9 seconds,
2. show that \(d = 1.5\),
3. find \(T\).